How to Check Your Car's Differential Gear Oil

Cars with rear-wheel drive have a differential, which works together with the two rear axles to allow the rear wheels to turn at the same speed when cornering. The differential is a set of gears (like a transmission) that is filled with gear oil. It's prudent to periodically check the differential gear oil to ensure there are no leaks.

Instructions

Difficulty: Moderately challenging

Things You’ll Need:

• Car Jacks
• Combination Wrench Sets
• Gear Oil
• Jack Stands
• Socket Sets

1. Park on level ground and shut off the engine.
2. Determine whether your car has front- or rear-wheel drive (see "Determine Whether Your Car is Front- or Rear-Wheel Drive" under Related eHows).
3. Locate the differential: it's under the rear middle part of the car, between the two rear wheels, and is shaped and sized like a pumpkin. There are axles (metal shafts) coming out of both sides of the differential that connect to each rear wheel.
4. Jack up both the front and back of the car and support the car using four jack stands. The front and back of the car must be level in order to check the differential gear oil.
5. Locate the bolt on the side of the differential. It will be facing toward the back of the car.
6. Choose a wrench or socket that fits the bolt and turn counterclockwise to loosen it. Remove it slowly.
7. The gear oil should be level with the bolt hole - it should dribble out, or you can reach in and check the level with your finger.
8. Add 90-weight gear oil if the level is low. It must be pumped into the differential. There are small pumps that attach to these plastic oil bottles.
9. Replace and tighten the bolt.
10. Remove the jack stands and lower the car.

Tips & Warnings

• Do not check the gear oil unless the entire car is level - you will get an inaccurate reading.
• If the differential is consistently low every time you check it, you probably have a leak. Look for wetness and make an appointment to see your mechanic.
• Never get under a car that is supported only by a jack - always use jack stands.
• Do not use regular motor oil - it's too thin. Use 90-weight gear oil.